This venerable method, albeit under slightly harsh conditions, delivered the product 3 in 52% isolated yield after chromatographical purification. Fortunately, several explorations rewarded us with finding proper conditions to access the cyclotrimer 3 by performing the reaction in o-dichlorobenzene ( o-DCB) at 180 ☌ under microwave irradiation using TiCl 4 as catalyst 16. The initial attempts towards the cyclotrimerization of 2 using SiCl 4 45 as a catalyst in ethanol failed only a trace amount of the desired product, 1,3,5-tris(9,9-dibutyl-2,7-dichloro-9 H-fluoren-4-yl)benzene (TFB, 3), was detected in the reaction mixture by MS spectroscopy. Our synthetic campaign was commenced with aldol cyclotrimerization of 1-(9,9-dibutyl-2,7-dichloro-9 H-fluoren-4-yl)ethan-1-one ( 2), which was prepared from commercially available 2,7-dichloro-9 H-fluorene in three steps (see Supplementary Information Section 1.2). Herein, we disclose the synthesis and properties of two classes of trichalcogenasupersumanenes with three chalcogen (sulfur or selenium) atoms and three methylene groups alternately embedded at the bay regions of p-HBC.įigure 2 depicts our three-step synthetic route for constructing these trichalcogenasupersumanene derivatives. These results fully reflect the difficulty to construct such curved supersumanene structures with smaller atoms, such as C and S. The success of HSHBC can be attributed to the bigger atomic radius of selenium atom and smaller strain. Fortunately, during this paper was being reviewed, Tan group reported the synthesis of hexa-selenium annulated p-HBC derivatives (HSHBC) 43 by using a similar strategy to TSHBC. have disclosed an elegant synthesis of tri-sulfur annulated p-HBC derivatives (TSHBC) 44 in which only three five-membered rings formed in bay regions, further full S annulation were not observed due to the high strain. However, experimentally bringing these imagined molecules into existence by chemical synthesis represents a gigantic challenge. Simple Chem3D simulation and normative density functional theory (DFT) calculation indicates a beautiful bowl-shaped geometry for these supersumanene derivates (i.e., X, Y = C, S, Se, etc.). Such bowl molecules feature a coronene core successively circumscribed by alternate hexagonal and pentagonal rings, we prefer to call it (hetero)supersumanene as a convenient trivial name based on similar structural characteristics and larger size compared with sumanene 12. It is of course interesting to imagine that if each of all six bay regions of hexa- peri-hexabenzocoronene ( p-HBC, also known as superbenzene) are bridged by one divalent group, it should formally constitute a large, compact, highly symmetric, zigzag rimed, and bowl-shaped architecture composed of 48 atoms and 19 rings in its bowl system (Fig. In the past decades, our group has been involved in the design and synthesis of new PAHs, naturally, bowl-shaped polyarenes have never escaped our consideration. have also been synthesized and sought as model compounds and partial structures for higher heterofullerenes. Hitherto the most literature-known hydrocarbon buckybowls were related to C 60 11, 12, 13, 14, 15, 16, 17, 18, 19 or C 70 20, 21, 22, 23, 24, 25, 26 fullerene fragments and their π-extended derivatives 27, 28, 29, 30. Owing to the huge inner strain of bowl-shaped hydrocarbons makes their synthesis a major challenge, the number of buckybowls is still relatively rare compared with flat PAHs. More significantly, some of the buckybowls could also serve as templates or seeds for the growth of single-walled carbon nanotubes 6, 7, 8, 9 having a controlled chirality and diameter and thus having uniform electronic properties useful in molecular electronic devices 10. Bowl-shaped polycyclic aromatic hydrocarbons (PAHs), often referred to as buckybowls or π-bowls, have emerged as attractive targets that captivate scientists from chemistry to materials science in light of their intriguing characteristics as well as potential applications in a diverse of scientific fields 1, 2, 3, 4, 5.
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